#scroll-bottom-btn {
    position: fixed;
    bottom: 100px;
    right: 20px;
    width: 50px;
    height: 50px;
    background-color: #333;
    color: #fff;
    border: none;
    border-radius: 50%;
    font-size: 20px;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    box-shadow: 0 2px 5px rgba(0,0,0,0.3);
    z-index: 9999;
    transition: background-color 0.3s, opacity 0.3s, visibility 0.3s;
    opacity: 1;
    visibility: visible;
}

#scroll-bottom-btn:hover {
    background-color: #555;
}

#scroll-bottom-btn.hidden {
    opacity: 0;
    visibility: hidden;
    transition: none; 
}